Numerous organic contaminants represent a danger to the environment and public health. Some classes of organic contaminants, (i.e. halogenated substances) have a high priority for concern, due to their chemical inertness and resistance to natural degradation in the environment. Halogenated substances maintain characteristics of persistency, harmfulness and toxicity for a long time (decades), with the possibility of bio-accumulation in various living species, posing permanent damage to living organism and in mankind. Some of these halogenated compounds (i.e. PCDDs and PCDFS) also present carcinogen, teratogen and mutagen risks.
In the last decades several methods for the treatment and the disposal of halogenated organic compounds have been proposed, such as controlled thermodestruction and the use of "secure" landfills. However, it has been found that, for the disposal of materials contaminated by toxic and halogenated compounds, these methods are not completely satisfactory, especially on large scales, and when the recovery of recyclable materials is desirable. In some instances, the correct disposal of wastes containing these compounds is impossible, since some countries are totally lacking in appropriate disposal systems (i.e. currently Italy).
Several chemical processes for the decomposition of halogenated organic compounds have been developed. Pytlewski and Smith, in their U.S. Pat. Nos. 4,337,368 and 4,236,090, demonstrated that polyhalogenated organic compounds were decomposed by reaction with a pre-formed organo-sodium reagent, such as sodium naphthalenide, NaPEG. In these ceases, the use of metallic sodium metal requires special handling procedures and specialized equipment. Even mere traces of water in suspension must be eliminated, so as to avoid dangerous side reactions that could cause explosions and fires.
Later, Brunelle of General Electric, in U.S. Pat. Nos. 4,351,718 and 4,353,793, proposed the removal of polychlorinated aromatic hydrocarbons dissolved in an organic solvent, such as transformer oil, by creating the solution with a mixture of polyethylene glycol or monocapped polyalkyleneglycol alkyl ether and an alkali metal hydroxide.
It has been found that such reactions require extended periods of time to reduce the concentration of halogenated contaminants, such as polychlorinated biphenyls (PCB's), to a level generally acceptable by the regulations effective in various countries.
Peterson of Niagara Mohawk Power Corporation in U.S. Pat. No. 4,532,028 proposed to reduce the level of halogenated aromatics in a hydrocarbon stream by treatment with an alkaline reactant in a sulfoxide solvent. This process involves a further purification step to remove the sulfoxide solvent, after decontamination. The resulting decontaminated fluid is reused.
In U.S. Pat. No. 4,632,742 and Eur. Pat. No. 0 118 858, Tundo disclosed a method for the decomposition of halogenated organic compounds by a reagent which consists of (a) polyethylene glycol, Nixolens.RTM., an alcohol or polyhydroxy compounds, (b) a base, such a carbonate or bicarbonate of an alkali metal or an alkaline earth carbonate and (c) an oxidative agent, such as Na.sub.2 O.sub.2 and BaO.sub.2, or a source of radicals in the absence of oxygen. This method is applicable to the decontamination of mineral oil, soil and various porous surfaces. But the use of sodium peroxide, or other oxidative agents, and the use of a source of free radicals, poses potential explosion and fire hazards. Also, this method can be prohibitively expensive because of the cost of peroxide.
Further, in U.S. Pat. No. 4,839,042 and Eur Pat No. 0 135 043, Tumiatti et al. described a continuous decontamination process with a dehalogenation bed, which is composed of a polyethylene glycol or a copolymer of various alkene oxides in a certain proportion, and an alkali alcoholate or alkaline earth. The components are adsorbed on certain solid carriers. However, this process was found to require a large amount of reagent and extended periods of time to reduce the concentration of halogenated contaminants, such as PCBs, to a generally acceptable level prescribed by current regulations.
In the Application for patent PCT/EP93/03609 dated Dec. 20, 1993, published on Jul. 7, 1994 as WO94/14504, Tumiatti presented a process for the removal of halogenated organic compounds from fluid and solid contaminated matrices, which allows the functional recovery of such fluids (mainly dielectric mineral oils in operation in electric transformers). The dangerous substances are easily decomposed from materials usable according to this dehalogenation process. The halogenated organic compounds are rapidly and completely decomposed by a reagent consisting in a non-alkali metal, a polyalkyleneglycol or a Nixolens.RTM. and a hydroxide or a C.sub.1 -C.sub.6 alcoholate of alkali metal or alkaline earth. This dehalogenating reagent overcomes the aforementioned deficiencies and gives more effective results than obtained by prior art methods using a reagent produced from an oxidative agent or a source of radicals. The dehalogenating reagent can be directly mixed with a fluid or solid matrix contaminated by halogenated organic compounds, under stirring and at a pre-selected temperature typically from 20.degree. C. to 150.degree. C. (preferably from 70.degree. to 120.degree. C.). The use of ultrasound and UV sources in the dehalogenation process increases the efficiency of the reaction 10-15%, and decreases the duration about 25%.
In particular, the reagent of WO94/14504, combined with porous solid supports (i.e. pumice), can become a fixed bed for the continuous removal of halogenated organic compounds in fluids contaminated by PCBs, by using a device of appropriate shape and dimension, such as a column and cartridge or a series of cartridges.
With the introduction of the dehalogenation process just described and its subsequent industrialization, it became desirable to find an optimized solution to improve the operation of the dehalogenation reagent. It also became desirable to provide for the recovery of the materials used to support the reagent, after the chemical dehalogenation of the PCBs and/or the destruction of the oxidized organic compounds, as an alternative to the traditional methods of disposal of the wastes generated.
Moreover, the industrial application of the decomposition process described above is not conveniently applied, or is totally inapplicable, to certain situations. Such situations include, for example, the destruction of ASKAREL (pure PCBs, or PCBs in mixtures with trichlorobenzene), oils highly contaminated by PCBs or halogenated substances, other contaminated synthetic fluids (i.e. silicones and esters), solids (soil, recyclable metals from machinery/equipment highly contaminated and destined to disposal by thermodestruction), and water based and gaseous matrices.